Grinder



p 1943- E. A. KOETHER 2,329,995

GRINDER Filed Jan. 24, 1940 ZSnventor Gttornegs Patented Sept. 21, 1943 GRINDER Emil A. Koether, Baltimore, Ma, assignor a Koppers Company, Pittsburgh, Pa, a corporation of Delaware Application January 24, 1940, Serial No; 315,438 I 16 Claims.

This invention relates to abrading and particularly to means and methods for improvin the accuracy of grinding operations by cooling the grinding elements as uniformly and as effectively as practicable and by substantially pre-- venting the transfer of heat from the grinding member to the supporting portions of the grinding machine, particularly the shaft bearings.

Arrest of the flow of heat from the grinding member to such supportingportions is a substantial factor in the attainment of the desired resulti Contrary to what might be expected, tests conventional mounts) results in enhanced heat v dissipation, as evidenced by marked reduction'in the temperature of the discharging ground articles. It is not here intimated that active cooling will not still further improve the operating congrinding disc is unevenly heated, its form is affected and inaccuracies result. Similarly, if the face plate on which the disc is mounted is heated, and particularly if it is unevenly heated, similar distortions are caused. Finally, transmission or heat to the bearings increases the lubrication problem and requires the bearings to be more freely fittedwhen cold than would be required if it could be assured that the bearings would runcool at all times.

The present invention involves the mounting of the grinding disc on the face plate in such a wayvthat the grinding disc is spaced .uniformly from the face plate, is cooled approximately uniformly on its back face and on its grinding face, and, hence, is conditioned to operate with the utmost precision so far as any distortion of the grinding disc itself is concerned. At this point ditions", particularly with heavy cuts. The 513- nificant fact is that arrest of heat flow from the grinding disc to its supporthas a beneficial effect which is always substantial and under some conditionsappears to be as important as stimulated air cooling. Both effects are present in the preferred embodiments of the invention.-

While the invention may be adapted to grinders of various types, it finds its greatest utility in connection with face' grinders in which an ab rasive disc is mounted on a ,face plate and the grinding is carried out on the plane surface of the grinding disc. ate heat quite rapidly, and this is particularly true of face grinders in which twoopposed discs afford a fixed gap through which the articles to be ground are fed in a substantially continuous stream. A typical example of such grinders is the type used for grinding the plane-faces of piston ring blanks andthe invention has been applied to this particular class of machine with marked success.

In the prior art, cooling during grinding has been provided for but it has been directed pri-' marily to safeguarding the article beingground against .undue heating. Very little consideration has been given in the past to cooling of the grinding elements themselves, or to the idea of maintaining uniformity of temperature as nearly as practicable -throughout the grinding disc.

Grinders of this type gener- The efiects of heat are numerous and diverse,

and'aiiect the grinding operation to an extent that was not appreciated until adequate'cooling was had.- Heating affects accuracy, If the connections betweenthe grinding disc and the face plate, the heat is dissipated before it reaches the face plate in any considerable degree.

As a consequence, only a negligibleportion' of the heat developed by the grinding operation is transmitted through the shaft to the bearings,

with the result that the bearings always under normal temperature conditions and can be fitted with'the utmost precision practicable in the bearing art, without risk that they will ever run hot.

All or these factors contribute to accuracy of grinding, but they have another and unexpected secondary result. The rate of development of heat increases rapidly. as the abrasive becomes finer, and the heat-effectsimpose a practicable limit on the fineness of the abrasive used in commercial grinding operationsin which a substantial' production rate is to be maintained.- Theelfective and uniform cooling characteristic of the present invention permits the 'use of much finer abrasive at commercial rates and actually permits the production by rinding operations of finishes not heretofore commercially produced except by the coarser lapping operations. Since theprodu'ction -rate of a grinder is many times Further, the face plate is similarly cooled and it may be remarked that by insulating the that of a lapping machine, the commercial importance of this secondary result is marked.

The invention contemplates the support of the disc on the face plate in such a way that the closest practicable approach to a continuous air gap between the disc and the plate is afiorded. It contemplates further, the fiow of air between the proximate faces of the grinding discs where two opposed discs are used and the flow of air between each disc and its face plate. In refined embodiments of the invention, the connections between the grinding disc and the faceplate are thermally insulated. While a useful and highly effective circulation can be produced by shrouding the grinding discs, drawing air from the shroud adjacent the peripheries of the grinding discs and admitting air particular cases. The path of flow of the air is much more important, but it, too, is subject to some variation to conform to limits imposed by the nature of the grinding machine or to meet special requirements incident to the form or material of the piece to be ground.

The preferred embodiment of the invention will now be described in connection with the accompanying drawing, in which:

Figure 1' is a view of the rear face ing disc showing the connecting bushings arranged according to a pattern known in the facegrinding art, but indicating the use of special connections according to the present invention.

Fig. 2 is anenlarged fragmentary section showing the connection between the disc of Fi u e 1 to the shroud at a diametrically opposite point,

better results can be secured by intensifying the air circulation. This can readily be effected by the use of hollow shafts through which air is delivered to the center of the disc. This air flows freely radially outward and discharges at the periphery of the disc. This direction of fiow is advantageous because the greatest heating occurs at the center of the disc, at which point'the coolest air is available. The desired circulation will be induced by a centrifugal blower action and may be intensified by shaping the connections between the disc and its face plate to the form of impeller blades, or, if preferred, a separate blower can be used to force air through the shaft. It is even possible to use an exhausting blower to draw air out .thro'ugh the shaft, but in such case, the direction of flow of the air in the interval between the disc and the face plate will not only be reversed but will be opposed to the natural centrifugal tendency. For that reason, the last-named arrangement is not considered desirable.

In referring to air as the cooling medium, its ready availability is a controlling consideration and the possible use of other gases is appreciated.

As indicative of the importance of the invention, it may be said that precision is appreciably improved, the over-all life of a grinding disc is increased by about one-fifth of its normal life as heretofore used, and the periods when the machine is outof operation for the purpose of dressing the discs are reduced by about one-third of the number of such periods formerly required. Thus, productivity of the grinding machine is substantially increased. The figures given are conservative and are exceeded in certain types of grinding operations.

The possibility of using finer grits on the wheels has already been suggested. This possibility arises from a reduced tendency to glaze. There is also less tendency of the grinding disc to assume what the operators call a smeary appearance. This appearance is attended with impairment of the grinding operation and while the exact cause is not known, it has been attributed on inconclusive evidence to fusion and flow of the bond in the grinding disc, particularly in resin bonded wheels.

In illustrating the invention, the effort will be to indicate controlling principles andto avoid the illustration of details of the grinding machine except where these enter into or affect, in one way or another, attainment of the desired results.

The manner in which the circulatory flow of air is induced is a secondary consideration and subject to variations to meet requirements of and the face plate'upon which it is mounted;

Fig. 3 shows a modified construction in which the separating pieces are formed on the face plate;

Fig. 4 is a further modification in which the separating members are independent of the grinding disc and of the face plate;

Fig. 5 is a fragmentary view of a similar portion of Figure 1, and indicating the use of independent separators such as those shown in Figure 4, to produce an impeller blade in the air gap between the grinding disc and the face plate.

Fig. 6 is an axial section through the grinding elements of a double disc .grinder constructed according to the patent to Koether, No. 2,169,252. dated August 15, 1939, and indicating one mode of applying the invention which has demonstrated marked utility. In this view the supporting bearings and drivingmotors are not indicated, the purpose being to simplify the view by limiting it to those feature which are directly involved in the cooling function;

Figure '7 is a rear face View of a modified form of grinder disc which maybe used in the structure of Figure 6 and which affords a definite impelling action designed to intensify the cooling effect; and

Fig. 8 represents the grinding elements of an opposed disc machine in which one of the shafts is hollow and serves as a conduit to deliver air under pressure for cooling both discs.

In Figure 1, II represents the grinding disc. This is provided as usual with an aperture i2 at its center and is provided at its rear face with a number -of tapped inserts 13. These inserts are of a form better shown in Fig. 2 and receive bolts 14 which pass through the face plate [5 of ordinary form and connect the grinding disc to the face plate rigidly while maintaining between the proximate faces of the plate and disc, that is, between the forward face of the plate and the rear face of the disc, an air gap which is substantially continuous.

The inserts l3, indicated in Figure 2, are formed to include the spacing elements, but this is not strictly necessary as alternative constructions are possible. the grinding disc alias inserts i3a which are tapped but 'which are flush with the rear face of the grinding disc. The face plate IE1: is formed with small bosses 18 through which the bolts Ida pass. The effect is the same as the construction shown in Figure 2.

Another alternative structure sometimes preferred is shown in Fig. 4, in which, instead of a boss l6 as shown in Fig. ,3, there is a separate insert l6b interposedbetween the disc Nb and the face plate l5b. In this case, the inserts 13b are identical with inserts I30 of Fig. 3. The disc of a grind- For example, in Figure 3,

2,829,995 lib can conveniently made of heat insulat ing material, and while the use of .this material is in the nature of a refinement, it is desirable.

In Fig. 5, which is a fragmentary view similar in proportion to Fig. 1, separate spacers 3b are used, but in lieu of certain of these, elongated spacers I60 are substituted. They span certain inserts in the two outer rows and form impeller blades.

In assembling the disc with'the face plate, the

conforming to the showing in Figure 2.

Any of the arrangements illustrated in Figs. 2 to 4 can be used without affecting the mode of operation of the device.

A pair of trackways 2'8 and. 29 extend between the discs .and are narrower than the interval between'the grinding faces. These serve to guide a series of piston .ringblanks, one of which ape spacers We can be set for either direction of rotation of the disc, that they may take the full line position, or, in lieu thereof, the dotted line position. This scheme involves no change in the spacing of the inserts indicated in Fig. 1, and offers a convenient means to secure an impeller action which may be adapted for either. direction of rottaion of the disc, due regard being had for the desired direction of flow of the air which is usually radially outward, but not necessarily so.

The arrangements so far described contemplate that the simple rotation of the grind ng' disc and its face plate will induce active flow of air through the interval between the face plate and the disc and usually th s air will enter the central aperture l2 and flow outward., Practically all grinding wheels are shrouded or enclosed and the shroud is provided with an air suction connection which, in the. old type of grinder was designed chiefly to carry away dust.

pears at'3l in atrave'rse diametrically through the interval between the grinding discs. The construction of the guide is not material to the present invention, but is clearly shown in the Koether patent above identified.

.Enclosing the grinding discs is a 'shrouding structure indicated at 32. This has at its bottom a large suction duct 33 which is connected through a dust-collecting means (not shown) According to the present invention, this oiftake A to an exhausting blower (not shown). An access opening atthe top is loosely covered by a cap 34 and air enters quite freely around this cover,.

and also through the slots which accommodate the guide tracks 28 and 29.

, Grinding discs rotate at quite high speeds and there is a moderate centrifugal impel-ling effect so that air is drawn in through the central aperture of the inner grinding member and flows thence outwardthrough the intervals between the various grinding members and their face plates.- The effect is 'to keep the grinding members cool and at uniform temperature, front and back. As indicating theeifectiveness oi such cooling, it may be said that a given grinder ofthe type illustrated in Figure 6 operating according to the invention, is so effectively cooled that immediately after it is stopped, it is possibl to place the hand. on the grinding surface even of the inner disc which is the one where highest Morton, No. 1,640,715, dated August 30, 1927, has

the axes of the discs oflset. The present invention can be used in such grinders. However, the offset disc type of grinder is being supplanted by the double disc type of grinder shown in the patent to Koether, above identified, in which there are two pairs of coaxial discs opposed to.

each other. The inner and outer discs of a given pair have their grinding faces in the same plane,

and they are driven at difierent speeds, and quite commonly in oppoflte directions.' These details depend on the type If finish desired.

The purpose of subdividing one grindin unit into two concentric parts driven at diiferentangular velocities is to secure higher lineal speeds in the central grinding area so that the disparity between grinding speeds near the center and at the outer limits will not be too great. A grinder of this yp is indicated in Fig. 6. 2| represents the outer shaft for the right-hand outer face plate 22, and represents the inner shaft for the right-hand inner face plate 24. There are similar left-hand units which bear similar reference numerals with the distinguishing letter (1. O

Mounted on the face plate 22 is an annular grinding element 25 and mounted on the face plate 24 is a smaller annular-grinding element 26. These have their grinding surfaces in the same plane and their axes are concentric, so that the inner grinding unit 26 turns concentricallywithin the outer unit 25. Each of the grinding elements is connected to its face plate by rigid spacing connections generally indicated temperatures always exist.

' Prior to the application of the invention, so

much heat was developed and transmitted through the shafts to; the bearings that after the machine had been running for two hours or more, the bearing housings were too hot to touch.

After the application of the invention, the bearingswere only slightly warm following many hours of running.

In Figure-7, a modified construction is' illustrated. This view represents the backs of the I two concentric grinding elements used in the structure of Figure 6. Curved spacers 35 are used and those for the outer grinding member 25 are set reversely as compared to th spacers 36 for the inner grinding member 26. It is here assumed that thetwo grinding members are to. run in-opposite directions. Po-accommodate reversal of direction of rotation, it i necessary only to reverse the spacer 35 and 36, either or both,

as the case may be. It will be observed that this assembly is possible because the spacing ofthe-connections is symmetrical in at least two circumferential series. of one blade reversed.

While the cooling circulation with a structure See the dotted showing such as that shown in Figs. 1 to 4 and 6 is satisfactory, for all practical purposes, and can be increased if desired by the simple expedient illustrated in Figs. 5 and 7, it is possible and would be desirable in certain extreme cases to mount a face plate on a hollow shaft and deliver air under pressure through the center of the face plate. A diagram-illustratingsuch a scheme is shown in Fig. 8. In this figure, the tubular shaft ll carries a face plate 42 and an axially aligned shaft 43 carries a face plate 44. The shaft 43 by the reference numeral 21, illustrated as commimication with the interior of the hollow shaft 4|. Some means of supplying air under pressure to the hollow shaft 4| may be used, for example, a rotary blower generally indicated at 48. This has a swivel connection at 49 with the end of the hollow shaft 4!.

Air delivered by the blower 48 would fiow outwardly between each grinding disc and its face plate and also between the proximate faces of the two opposed grinding discs. The spacing of the connections between the grinding discs and the face plates may follow the showing in any of the various figures. If the arrangement of Fig. 5 be adopted, the efiect would be either to assist the blower 48 or even to render it unnecessary.

The purpose in illustrating various modified forms is to suggest the wide latitude possible in applying the invention. The inventive concept is not limited to any particular manner of circulating the air. It resides rather in the idea that the grinding discs are supported in such a way that a heat-insulating air gap is afforded between the disc and the supporting face plate and some means is provided to'cause or permit circulatory flow of air. The effect is to dissipate the heat and maintain the grinding discs at substantially uniform temperature throughout the grinding operation. The result is to cause the discs to run cooler and truer. The interception of the heat which would otherwise be conducted to the shafts and bearings performs very valuable functions which have already been described in considerable detail, and which are useful irrespective of intensive air cooling.

What is claimed is:

1. A grinding unit comprising a rotatable face plate; a face grinding disc approximately coextensive with said plate; spaced connections rigidly connecting said plate and disc; spacing means associated with said connections and formed to preserve a substantially continuous air gap between the plate and disc, at least some of them being formed to serve as air impelling means when the unit is rotated; and means forming an air passage communicating with said air gap near the axis of rotation of the unit.

2. The combination defined in claim 1 in which at least the spacers having impelling character-.

istics are reversible to reverse their impelling characteristics and thus permit alternative assemblies for opposite direction of rotation of the unit.

3. The combination defined in claim '1 in which the air passage leads through the face plate.

4. In a grinding machine, the combination of a rotatable face plate; a face-grinding disc approximately coextensive with said plate; spaced connecting means rigidly connecting said plate and disc and serving to preserve an approximately continuous air gap between the plate and disc; and air circulating means for causing air to pass continuously through said air gap.

5. A grinding machine comprising a rotatable face plate; a face-grinding annulus approximately coextensive with said plate; spaced connecting. means rigidly connecting said plate and annulus and serving to preserve an approximately continuous air gap between the plate and annulus; work-guiding means; a shroud enclosing said plate and annulus and said work-guiding I means; a suction offtake leading from said shroud at a point adjacent the periphery of said annulus and plate; and means for admitting air to said shroud and so directing its fiow that at least a portion of such air passes through the center of the annulus to the air gap and flows radially outward through the air gap to said offtake.

6. A grinding machine comprising a rotatable hollow shaft; a. face plate carried thereby; a rigid face-grinding disc of substantial thickness and composed of abrasive material, said disc being approximately coextensive with said face plate; spaced connecting means rigidly connect ing said plate and disc and arranged to preserve an approximately continuous air gap between the plate and disc; and means for circulating air through said shaft to'the center of said air gap whereby an outward flow of air through the air gap is assured.

7. A grinding machine comprising two rotatable grinding units mounted in face-to-face relation with an interval between the same, each grinding unit comprising a rotatable face plate, a face grinding annulus approximately coextensive with said plate, and spaced connecting means rigidly connecting each annulus with the corresponding plate and serving to preserve an approximately continuous air gap between the plate and annulus; shafts upon which said face plates are'respectively mounted, at least one of said shits being hollow; and means for delivering air under pressure to said hollow shaft whereby air is supplied at their centers to the air gaps between the face plates and annuli, and to the interval between the proximate faces of the annuli.

8. The combination with the structure defined in claim 'I of guiding means for work pieces, a shroud partially enclosing said guiding means and enclosing said grinding units, and an air ofitake leading from said shroud at a point adjacent to the peripheries of said grinding units.

9. The method of controlling heating effects in a rotary face grinding disc of substantial thickness and composed of abrasive material, which comprises so mounting the disc for rotation that its rear and front faces are exposed over substantially their entire superficial areas,

and circulating confined streams of air over both v surfaces.

10. The, method of controlling heating effects in a rotary face grinding disc of substantial thickness and composed of abrasive material, which comprises so mounting the disc for rotation that its rear and front faces are exposed over substantially their entire superficial areas, and circularting confined streams of air from the center outward over both surfaces.

11. A grinding machine comprising a rotatable tial thickness and composed of abrasive material, said disc being approximately coextensive with said plate; spaced connecting means rigidly connecting said plate and disc and arranged to preserve an approximately continuous heat insulating zone between the plate and disc; and means to guide articles to be ground in av path of limited width across and in contact with said disc, whereby only a portion of the disc is active at any one time.

' 12. The combination defined in claim 11 in which the spaced connecting means have, heat insulating characteristics.

13. A grinding machine comprising a rotatable faceplate; a rigid face grinding disc of substantial thickness and composed of abrasive material, said disc being approximately coextensive with said plate; spaced connecting means rigidly connecting said plate and disc and arranged to preserve an approximately continuous 7 air gap between the plate and disc: means pro-4 viding ,an air passage leading to such air gap near the axis of rotation of the disc; and means to guide articles to be ground in a path of limited width across and in contact with said disc, whereby only a portion of the disc is active at any one time.

14. The combination defined in claim 13 in which the air passage leading to the air gap takes the form of a. central aperture through said disc.

15. A grinding machine comprising two rotatable grinding units mounted in a face-to-face coextensive with each of said platesfand spaced relation with an interval between the same through which interval the articles to be ground are passed, each grinding unit comprising at least two coaxial independently rotatable face plates, rigid face grinding annuli approximately connecting means rigidly connecting each annulus with the corresponding plate and arranged to preserve an approximately continuous heat insulating zone between the plates and the annuli.

' EMIL A. KOE'I'HER. 

